1. Technical Field
The present invention relates to an optical image system. More particularly, the present invention relates to a compact optical image system applicable to electronic products.
2. Description of Related Art
In recent years, with the popularity of mobile products with camera functionalities, the demand for compact optical image systems is increasing. The sensor of a conventional photographing camera is typically a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor Sensor). As advanced semiconductor manufacturing technologies have allowed the pixel size of sensors to be reduced and compact optical image systems have gradually evolved toward higher megapixels, there is an increasing demand for compact optical image systems featuring better image quality.
A conventional compact optical image system in a portable electronic product typically utilizes a three-element lens structure. Such a conventional optical image system has a first lens element with positive refractive power, a second lens element with negative refractive power and a third lens element with positive refractive power. The first, second and third lens elements are arranged in this order from an object-side to an image-side. While the three-element lens structure is compact, it is not able to produce high quality images.
Further, another conventional compact optical image system provides a four-element lens structure. The first lens element and the second lens element of the four-element lens structure are two glass spherical lens elements which are attached to each other to form a doublet lens for eliminating chromatic aberration. However, this lens structure requires a longer total optical track length caused by insufficient degrees of freedom in setting system parameters due to too many spherical lenses allocated. Moreover, it is not easy to attach the glass lenses, and thus the manufacturing process for forming the glass doublet lenses is difficult.